Even low levels of heavy metals (for example arsenic, lead, cadmium, mercury, etc.) in drinking water are considered detrimental to a person's health, and in the case of infants, are believed to impede intellectual development. Recognizing these hazards, the Environmental Protection Agency (EPA) has established limits on the presence of heavy metals in drinking water. For example, no more than 15 parts per billion (15 ppb) of lead may be present in public water systems. The EPA and the World Health Organization (WHO) have established that a safe threshold for arsenic levels in drinking water is less than 10 micrograms per liter (ppb) of arsenic. In addition, industrial water streams must contain less than 0.5 ppm of heavy metals before the water can be discharged.
In addition to reducing the heavy metals to acceptable EPA levels, it is desirable to improve the taste, odor and smell of drinking water by removing chlorine, ionic metals, organic molecules and colloidal particles. Ion exchangers, both organic and inorganic, including crystalline molecular sieve zeolites, are known to remove certain metals from aqueous systems such as drinking water. Activated carbon is also used in water purification or remediation processes. Activated carbon improves taste, odor and smell by adsorbing ionic metals, organic molecules and colloidal particles and also removes chlorine.
The purification of drinking water is often accomplished at its point of use, such as under-the-counter, on-the-counter, whole house systems, under-the-tap, or free standing gravity flow carafe type devices. For industrial/commercial applications, packed bed systems are typically used.
Activated alumina is known to have some capacity for the adsorption of arsenic from water. One of the drawbacks associated with alumina is that the arsenic removal capacity is relatively low and large amounts of media are needed to provide sufficient life for the adsorption column.
A material comprising lanthanum oxides and alumina can be used for arsenic removal, but lanthanum oxides are too expensive for the treatment of large volumes of water. Recently, another media containing aluminum oxide and manganese oxide, sold under the trade designation AQUA-BIND, removes higher levels of arsenic over standard activated alumina.
There is an ongoing effort to develop improved products which meet or exceed EPA requirements for heavy metals removal as well as improved taste, color and odor, and have flow rates which are commercially acceptable.